1. Field of the Invention
This invention relates to heat pumps and pressure pumps of the type in which hydride-forming materials are thermally cycled in order to achieve the desired pumping action. More specifically, this invention relates to hydride pumping devices in which the hydride-forming material is cyclically transported between a high temperature/high pressure environment and a low temperature/low pressure environment. Both continuously operating and moving batch hydride transport systems are disclosed.
2. Description of the Prior Art
Various types of pumping devices employing hydrides have been proposed to pressurize hydrogen (pressure pumps) and to transport heat energy from a given input temperature to a higher output temperature (heat pumps). Hydrides have the ability to chemically store large quantities of hydrogen in a concentrated form at a variety of temperatures and pressures, and then to release the stored hydrogen when heat is added to the hydride. Numerous hydride-forming materials have been identified, and recently various hydrides, especially metal hydrides, have received considerable attention for potential use in heat and pressure pumps. As used herein, the term "hydride forming material" is used to refer generally to materials capable of absorbing and desorbing hydrogen, in both the hydrided and the dehydrided states.
In U.S. Pat. No. 4,055,962 to Terry, a hydride heat pump is disclosed in which a number of reactor vessels are used to contain fixed beds of hydride-forming materials. These vessels and the contained hydrides are thermally cycled to hydride and then dehydride the hydride-forming materials. Individual vessels are cycled in staggered sequence so that an approximation of continuous operation is provided.
Similarly, U.S. Pat. No. 4,044,819 to Cottingham discloses another hydride heat pump which also employs fixed beds of hydride contained in reactor vessels. Once again, the entire reactor vessel is thermally cycled in order to achieve the desired thermal cycling of the contained hydrides. The disclosed device operates in a cycle in which each bed of hydride is used to alternately absorb and then desorb hydrogen, and once again, semi-continuous operation is only achieved by multiplying the number of hydride beds and operating them in staggered phase.
U.S. Pat. No. 3,943,719 to Terry and Schoeppel discloses yet another discontinuous, fixed batch hydride pump in which reactor vessels are thermally cycled and multiple, staggered-cycle, hydride beds are used to achieve continuous pressure pumping.
Significantly, none of the above-referenced prior art is capable of achieving continuous pumping action without resorting to multiple, staggered cycle hydride beds. Such staggered bed systems are relatively complex devices employing multiple valves, reactor vessels, and heat exchangers. In addition, the art does not contemplate the use of means for avoiding the thermal cycling of reactor vessels. In each case, both the reactor vessels and the contained hydrides are thermally cycled together. This thermal cycling of major structural components brings with it several disadvantages. Sensible heat is required to periodically heat the thermal mass of the reactor vessels. This heat is only partially recovered as the temperature of the vessels is cycled, resulting in a reduction in the thermodynamic efficiency of the hydride pump. Secondly, the thermal cycling of the reactor vessels will, in many cases, induce severe mechanical stress and strains which may result in accellerated mechanical failure. Furthermore, these reactor vessels are routinely exposed to hydrogen, and thermal cycling in the presence of hydrogen accelerates hydrogen embrittlement of many metals. Thus, hydrogen embrittlement of reactor vessels and associated maintenance problems are exacerbated.